Flat Base -vs- Boat Tail bullets.

Cass

Not exactly a new topic, and has possibly come up before, but was doing a bit of zeroing on the range today, and was surprised at the results i got.

I was initially testing a mod on a rifle. When it was all done i fired a couple of shots to re-zero without the mod. I have some 185 gr Berger BT bullets. When i fired them the hit approx 0.25 - 0.5 inch right of the bull.

The wind was blowing fairly strong with 15-18mph almost at 9 o'clock, and then the occasional gust. I then switched back over to the "regular" ammo. 180gr Federal. These are flat based bullets, but with a similar muzzle velocity, and weight i expected a similar performance.

Fired 2 rounds, and while the height was spot on compared to the BT bullets they were 2.75 & 3.25 inches to the right. That was between 7-12 times further out than the BT bullets.

All this was done at 100 yards hence the surprise. I really thought that a .308 bullet would stand up the wind a bit better, not to mention that it was a heavy bullet. So it settled any doubt about the performance abilities of BT over Flat base.


Was wondering if anyone has had similar experiences or tried something along the same lines. Does it hold true for all calibers? Do you not notice a difference until out at longer distances?

tac foley

Read this - http://www.snipercentral.com/forums/viewtopic.php?t=25999

tac

zeissman

Thats a big difference.
Do both bullets shoot to the same point of impact in calm condititions ?
What sort of wind drift should you have going by the balistic tables for each bullet ?

tac foley

A boat-tail design reduces the so-called parasitic drag at the base of a projectile by causing less air cavitation. The same principal is applied to long-ranger artillery projectiles. In that case, the range of a given projectile can be extended by having the partial vacuum that occurs at the base of the projectile in flight, and the air turbulence caused by trying to fill it, replaced by a gas with the same density as the air. This is done in an arty projectile by having a small gas generation pyrotechinic burning while the projectile is in flight. The projectile is then described as having a 'base-bleed' or, in full - ERBB - Extended range base bleed.

Obviously we can't do the same with a small-arms bullet, although is has been noted over the years that matching tracer rounds to ball has always been a mite tricky due to the rather improved performance over longer ranges of the tracer bullet by comparison with the plain ball. A reduction in the diameter of the bullet at the base was therefore a plausible improvement. Some boat-tailed bullets have markedly small, or longer, if you prefer, boat-tails than others - the school is still out on this one, so compare Berger with JLK and Sierra with Nosler and Hornady and make up your own mind.

Suffice it to say that in full-bore centre-fire, out to about 600m/yds, the flat-base bullet is going to be the winner - proven over a hundred years ago here in UK and USA when the new-fangled spitzers were finally more widespread than hitherto.

The science of ballistics is the interpretation of the laws of physics - they do not change, all that changes is our appreciation of them and making ammunition that maximises the knowledge we gain from usefully applying them.

tac

Cass

zeissman wrote: »

Thats a big difference.

I knew the BT would be a better round, hence more accurate, but that's what surprised me was the amount of drift of the FB.

Do both bullets shoot to the same point of impact in calm condititions ?

Exactly, yes. That's why i use them. The 180 FB, for hunting, and the 185 BT for comps. They have the same POI at 100 in both elevation, and windage at 100, and 200 yards. Have no shot them at 300 yet.

What sort of wind drift should you have going by the balistic tables for each bullet ?

For the BT i'm looking at 0.75" in an 18 MPH full value wind. For the FB i'm giving 1.75" in the same conditions.

While the BT performed as expected, if not marginally better, the FB was almost double the predicted drift.

Both rounds are similar in OAL, MV, etc. So the only difference i can put this down to was the design of the bullet. That's why i was asking about similar experiences. Would be interested to know if the real world effects are the same for other calibers.

Cass

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fish slapped

WoW! Nice one EZ...

That's a fair difference. I never would of thought it was that much. I'll certainly be paying more attention to what ammo I'm feeding my guns especially the 223 as I would expect even more of a difference given the lighter bullet.

If I remember correctly that American eagle stuff is all flat base. What other ammo is Flat Base???

EWQuinn

"For the FB i'm giving 1.75" in the same conditions."

This is about what the Sierra Manual and other ballistics tables would indicate. However I will say that I have experienced similar mysterious results at distances where the deflection should not be that much.

Cass

It's a strange one alright.

So even though the ballistic calculator said that the flat based bullets would suffer from more deflection it underestimated the amount by 50%. At 100yards that's not great, but my concern was at 200+ yards.

It's the difference between missing with a shot or worse again injuring an animal.

Goes to show BCs, and other such tools are exactly that. Tools. Not guarantees. Always pays to do your own checking.

Merch

tac foley wrote: »

Suffice it to say that in full-bore centre-fire, out to about 600m/yds, the flat-base bullet is going to be the winner - proven over a hundred years ago here in UK and USA when the new-fangled spitzers were finally more widespread than hitherto.
tac

Why? dont you mean the spitzer type? or BT? they're the same aren't they?
You say the flat base bullet would be the winner? is that the case out to longer ranges? I thought the effects/performance of a flat based bullet out to longer ranges would be even worse, than at shorter ranges?

Is that a typo? if not aren't people saying the BT performs better?

edit, just reading the link

It still seems to suggest BT are more accurate out to longer ranges?

ejg

One thing is for sure, I prefer to hunt with a 1 moa rifle/ammo combo filled with high BC BT bullets rather than
a 1MOA rifle/ammo combo filled with low BC flat base. Why would I choose the worse?
Use science.....
edi

Merch

ejg wrote: »

One thing is for sure, I prefer to hunt with a 1 moa rifle/ammo combo filled with high BC BT bullets rather than
a 1MOA rifle/ammo combo filled with low BC flat base. Why would I choose the worse?
Use science.....
edi

my level of knowledge on the subject will become more apparent, from now!
a high BC is low drag resistance? i assume.
i also assume they cost more?

ejg

Merch wrote: »

my level of knowledge on the subject will become more apparent, from now!
a high BC is low drag resistance? i assume.
i also assume they cost more?

Yes higher BC value = lower drag and lower wind deflection.
Although I said high bc are "better" I would still prefer an
accurate flat base hunting bullet over a not so accurate BT.
Or in my little lever action that will be used under 100yds it
wouldn't make much difference either. As an allround hunting rifle that
will be used over 300yds at times I would prefer accurate BT's.
edi

Glensman

ANother plus for BT is that they are a LOT easier to reload...